Method for producing regenerated cellulose products



United States Patent 3,217,068 METHOD FOR PRODUCING REGENERATED CELLULOSE PRODUCTS Nicolas Drisch, Paul Herrbach, and Henri Rodier, Paris,

France, assignors to Chimiotex S.A., Geneva, Switzerland, a corporation of Switzerland No Drawing. Filed Nov. 14, 1962, Ser. No. 237,711

1 Claim. (Cl. 264-38) This invention relates to a process for producing regenerated cellulose filaments having improved characteristics.

In French Patent No. 1,266,492 of April 22, 1960, a process is described for the manufacture of fibers, filaments, etc. (of the generic group of polynosics) having advantageous mechanical characteristics, obtained by spinning of high gamma inxex and DP viscose, in a cold bath containing small quantities of an aldehyde.

This invention relates to the elimination of hydrogen sulfide from baths containing an aldehyde, notably formaldehyde.

It has been found that spinning according to the process specified in the above patent becomes increasingly difiicuit and that the quality of the products obtained worsens as the bath becomes loaded with products resulting from the combination of formaldehyde with hydrogen sulfide. The products formed constantly alter spinning conditions, particularly stretchability of the gel, which renders the operation of the process difficult. When the bath is loaded with these products in the first stage of condensation, it becomes discolored and emits an unpleasant odor. When the final insoluble condensation product appears, i.e., trithiane, the bath becomes clouded and trithiane is deposited on the equipment, notably on the spinnerets, the useful life of which is thus substantially reduced.

In an acid medium, formaldehyde combines with the hydrogen sulfide produced by the decomposition of sulfide by-products contained in the viscose. At the outset there is probably a formation of soluble hydroxymethylmercaptan which is then converted by condensation into insoluble trithiane. The formation of trithiane is moreover accelerated by temperature rise.

The formation of trithiane being very rapid and continuous, filtration of the bath is no longer sufiicient to purify it, the clear bath coming out of filtration quickly becoming clouded again. At the outset of its formation, trithiane is produced in a form which is difficult to filter. Another disadvantage resulting from the formation of trithiane is the impoverishment of formaldehyde in the bath since, each molecule of hydrogen sulfide which is liberated during spinning fixes a molecule of formaldehyde in insoluble form. The result is a formaldehyde consumption several times greater than would be necessary to maintain the content sought in the bath. Consequently it was sought to reduce the formation of products of the combination of hydrogen sulfide and formalde hyde to a substantial extent.

According to this invention, it has been found possible to extract from the bath a high percentage of the hydrogen sulfide produced during spinning immediately after its formation, without at the same time eliminating the formaldehyde present in the bath. The process consists of bringing in close contact with the bath in a period of less than 1 hour and preferably less than minutes for example within a period of three minutes, a volume of air at least ten times and preferably at least 100 times greater than that of the bath after the bath has been loaded with hydrogen sulfide by decomposition of the viscose from the spinneret. The need to extract hydrogen sulfide from the bath very rapidly in order to prevent it from reacting with the formaldehyde is evidenced by the following table 3,217,068 Patented Nov. 9, 1965 which indicates, as a function of time, the percentage of H 8 recoverable in a bath at 20 C. which contains initially 8.3 g./l. of formaldehyde and variable quantities Dill-1 S.

8.3 g./l. Formalde- 8.3 g./l. Formalde- Time, min. hyde +237 mg. of hyde +53 mg./l.

H28, percent H S H S, percent H S recoverable recoverable The spinning bath can be brought in contact with air by known mechanical means, but it is necessary to obtain a complete emulsion from the air used in the bath treated so as to form a stable foam for several minutes. It is advantageous, in order to facilitate formation of this foam, to add to the spinning bath a surface-active product, so as to reduce the surface tension of the bath.

The example cited below, without being limitative, illustrates the process according to the invention:

A viscose prepared in known manner, containing 6% cellulose and 6% total alkali, calculated in sodium hydroxide, using 60% carbon disulfide in relation to the weight of the initial cellulose, is extruded into a 20 bath of composition:

NH2SO4 containing, in addition, 1% of formaldehyde and 0.1% of a surface-active agent.

The bundle of filaments coming from the spinneret is guided into a tube or narrow channel making it possible to collect the bath used very shortly after it has reacted with the viscose.

This used bath, which contains 10.5 mg./l. of hydrogen sulfide, is then introduced by gravity or by pumping or preferably by suction into a device known as an ejector in the form of a Venturi tube, consisting of two outlet tubes in the same axis, one of the outlet tubes discharging air under pressure exceeding atmospheric pressure. Such device generates a vacuum. The spinning bath is introduced into this device and carried along by the air jet producing a violet turbulence on encountering said jet, which emulsifies the air in the bath. The emulsion obtained disappears beyond the zone of turbulence. The elimination of the emulsion can be accelerated by known means usually employed for this purpose. The device is equipped with cocks or valves making it possible to regulate the flow of air or flow of bath.

The bath, which is separated after destruction of the emulsion, is practically freed of the hydrogen sulfide it contained (0.5 to 1 mg./l. remains) and its formaldehyde content has not varied. No formation of trithiane is observed in the bath so treated, while in the untreated bath a large formation of trithiane is observed at the end of a few hours.

According to one Variant, the hydrogen sulfide produced during spinning can also be eliminated by spraying the bath in fine drops on top of a tower in which a suitable flow of air circulates in the opposite direction. The tower can be filled with suitable materials assuring a large running surface and increasing the contact surface between air and bath.

What is claimed is:

In a process for eliminating from an acid viscose spinning bath containing formaldehyde, the hydrogen sulfide which is formed during the spinning operation which comprises continuously withdrawing the bath containing the hydrogen sulfide from the reaction zone and immediately introducing air into said bath while so withdrawn in the presence of a wetting agent to cause the air to rise to the surface of the bath as a foam in which the hydrogen sulfide is occluded, and removing the foam from the bath the improvement which comprises effecting the air treatment before substantial reaction takes place and in less than 10 minutes after the initial formation of the hydrogen sulfide.

References Cited by the Examiner UNITED STATES PATENTS 2,352,519 6/44 Costa et a1 26438 2,394,957 2/46 White 18--54 2,413,102 12/46 Ebert et a1. 264-38 2,659,102 11/53 Rarick 26438 2,918,348 12/59 Gage 18-54 2,937,070 5/60 Cox 264 FOREIGN PATENTS 925,741 5 63 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner. MORRIS LIEBMAN, Examiner. 

